This work compares alternatives for the production of high ductility ADI, austempered from an intercritical austenitizing temperature range, with a microstructure of ferrite + ausferrite. Different initial microstructures were selected, including ferrite, pearlite, pearlite + ferrite, martensite and ausferrite. The samples were austenitized within the intercritical zone (795 °C) for different times (up to 12 h) and then austempered at 350 °C. The evolution of the formation and distribution of ferrite and austenite during the austenitizing process for the different initial microstructures was studied. For the selected austenitizing temperature, all of the initial microstructures produced 30% ferrite (70% ausferrite) in the final microstructure (after 12 h). The mechanical properties depend upon the distribution and refinement of the ferrite and ausferrite areas. Spheroidized carbides from pearlite are not completely dissolved during intercritical austenitizing for 2 h. Graphite nodules are an important source of carbon for the austenite formed from starting microstructures of ferrite, pearlite + ferrite and pearlite with grain boundaries being the main pathway for carbon diffusion. Austenitizing started away from the graphite nodules at eutectic cell boundaries due to Si segregation. For starting microstructures of ferrite, pearlite and pearlite + ferrite, a homogeneous distribution of austenite does not occur. Rather, it is concentrated on eutectic cell boundaries and ferrite grain boundaries with large areas of ferrite around the graphite nodules. For starting microstructures of martensite and ausferrite, carbon is evenly distributed and quickly dissolved, resulting in a homogeneous distribution of austenite and ferrite with the best combination of strength and ductility.

中文翻译：

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具有双重显微组织的奥氏体球墨铸铁：初始显微组织对奥氏体化过程的影响

这项工作比较了在临界奥氏体化温度范围内奥氏体化的高延展性ADI的替代产品，以及铁素体+奥氏体的微观结构。选择了不同的初始微观结构，包括铁素体，珠光体，珠光体+铁素体，马氏体和奥氏体。将样品在临界区（795°C）中奥氏体化不同的时间（最多12小时），然后在350°C的温度下进行奥氏体化。研究了不同初始显微组织在奥氏体化过程中铁素体和奥氏体的形成和分布的演变。对于选定的奥氏体化温度，所有初始显微组织在最终显微组织（12小时后）中均产生30％的铁素体（70％的铁素体）。机械性能取决于铁素体和奥氏体区域的分布和细化。珠光体中的球状碳化物在临界奥氏体化2 h时并未完全溶解。石墨结核是奥氏体的重要碳源，奥氏体由铁素体，珠光体+铁素体和珠光体的初始微观结构形成，而晶界是碳扩散的主要途径。由于Si的偏析，在共晶晶胞边界处从石墨结节开始了奥氏体化。对于铁素体，珠光体和珠光体+铁素体的初始微观结构，不会发生奥氏体的均匀分布。相反，它集中在共晶晶胞边界和铁素体晶粒边界上，在石墨球周围有大面积的铁素体。